Magnetic field sensors can be used to sense an angle of rotation of a shaft. For example, a magnet can be mounted on the shaft such that it rotates with the shaft, and a magnetic field sensor can be arranged proximate the magnet in order to sense a magnetic field induced by the magnet as it rotates with the shaft. When the magnetic field sensor is mounted next to or adjacent the shaft, i.e., off of the axis of rotation of the shaft, the sensor is often referred to as an “off-axis” magnetic field angle sensor. Off-axis magnetic field angle sensors often are implemented when the end of the shaft is unavailable as a location for the sensor or there simply is not space available on the shaft. An “on-axis” magnetic field sensor is one in which the sensor is mounted at or near the end of the shaft, generally in-line with or on the axis of rotation. Examples of off-axis and on-axis sensors are perpendicular angle sensors and axial angle sensors.
Axial angle sensors are magnetic field angle sensors that utilize the axial magnetic field component to infer the rotation angle. The sensors perform optimally with fields that are linearly varying in two components and must be arranged in an off-axis configuration because the axial magnetic field component cannot be detected on the axis of rotation for many types of common magnets such as diametrically magnetized magnets of rotational shape. An additional feature of axial angle sensors is that the sensors are robust against external magnetic disturbances. Perpendicular angle sensors, on the other hand, perform optimally with homogeneous magnetic fields and utilize radial and azimuthal magnetic field components to infer a rotation angle. The perpendicular angle sensors can be manufactured for robustness against assembly tolerances and can be arranged in an on-axis configuration. In many applications there is a general preference for magnetic field angle sensors, whether off- or on-axis or axial or perpendicular, to be inexpensive while also being robust with respect to external magnetic fields and other disturbances. A drawback of some perpendicular angle sensors, then, is that they are not robust against external magnetic fields and other disturbances. While axial sensors are more robust with respect to these disturbances, axial sensors are more sensitive to assembly tolerance errors. Other drawbacks to conventional approaches include the inability to provide a robust sensor that is capable of detecting angles over a full 360 degree range. In general, therefore, there are numerous drawbacks associated with conventional magnetic field angle sensors.